Check litter: At each place, check the litter around - click on them. Some trash might be hiding money like the Euros hidden on the litter in front of the Casa dei Giochi at Campo Santa Margherita or at Campo Santa Maria Formosa.

So go to different locations and check trash that are on the ground especially those mentioned above.

your cursor will not change to a hand or anything. Just move your cursor over piles of leaves & junk on the ground & click away all around it. If there is a coin there, it will come flying out & will be added to your existing money.